Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel. As a result, kinds of applications using the secondary battery are being increased owing to advantages of the secondary battery, and hereafter the secondary battery is expected to be applied to more applications and products than now.
As kinds of applications and products, to which the secondary battery is applicable, are increased, kinds of batteries are also increased such that the batteries can provide outputs and capacities corresponding to the various applications and products. Furthermore, there is a strong need to reduce the size and weight of the batteries applied to the corresponding applications and products.
For example, small-sized mobile devices, such as mobile phones, personal digital assistants (PDAs), digital cameras, and laptop computers, use one or several small-sized, light cells for each device according to the reduction in size and weight of the corresponding products. On the other hand, medium- or large-sized devices, such as electric bicycles, electric motorcycles, electric vehicles, and hybrid electric vehicles, use a battery module (or “battery pack”) having a plurality of cells electrically connected with each other because high output and large capacity is necessary for the medium- or large-sized devices. The size and weight of the battery module is directly related to the receiving space and output of the corresponding medium- or large-sized device. For this reason, manufacturers are trying to manufacture small-sized, light battery modules.
The conventional medium- or large-sized secondary battery module is constructed in a structure in which a plurality of unit cells are received in a case (housing) having a predetermined size, and the unit cells are electrically connected with each other. At the outside of the case are mounted a plurality of circuit units for sensing the voltage, the current, and the temperature of the unit cells and controlling the operation of the battery.
It is required for the medium- or large-sized secondary battery module to have a different structure from a small-sized battery due to the structural or use characteristics thereof.
The medium- or large-sized secondary battery module uses a plurality of unit cells to provide high output and large capacity. Especially, all or at least some of the unit cells are connected in series with each other to provide high output. Consequently, when some of the unit cells are damaged due to overcharge, overdischarge, overcurrent, overheating thereof, the entirety of the battery module may catch fire or explode through a chain reaction. Also, the malfunction of some unit cells may cause the malfunction of the entirety of the battery module. For this reason, there is used a device for continuously sensing and controlling the voltage and/or the current of each unit cell and the temperature of the whole battery module.
Generally, wires are directly connected to the electrode terminals of the unit cells or connected to electrical connecting members of the electrode terminals such that the voltage and/or the current of the unit cells can be sensed and controlled by a circuit part, such as a battery management system (BMS). Consequently, a large number of wires are necessary to sense the voltage and the current of the unit cells with the result that the assembly process of the battery module is complicated, and the number of defective battery modules is increased.
Generally, rectangular cells or pouch-shaped cells, which can be stacked with high integration, are used as the unit cells of the battery module. Preferably, the pouch-shaped cells are normally used as the unit cells, since the pouch-shaped cells are light and inexpensive. Each pouch-shaped cell includes an electrode assembly, which comprises a cathode, a separation film, and an anode, mounted together with an electrolyte in a sealed pouch-shaped case, which is made of an aluminum laminate sheet. The pouch-shaped cell has a structure in which small plate-shaped electrode terminals are exposed at the outside of the electrode assembly. However, several problems are raised when the small plate-shaped electrode terminals are electrically connected with each other. Generally, the electrode terminals are connected with each other using wires, metal plates, or bus bars by welding, but it is difficult to electrically connect the plate-shaped electrode terminals with each other by welding. In a conventional art, holes necessary to accomplish the electrical connection are drilled in a printed circuit board, the electrode terminals of the unit cells are inserted through the drilled-holes, and then the electrode terminals of the unit cells are attached to the printed circuit board by welding. However, the mechanical strength of the electrode terminals is low. As a result, it is difficult to accurately insert the electrode terminals of the stacked unit cells at predetermined positions, and, at the same time, it is also difficult to insert the electrode terminals of the stacked unit cells through the drilled-holes of the printed circuit board.
Also, the medium- or large-sized secondary battery module is used in various devices, such as electric bicycles, electric vehicles, and industrial equipment. These devices are subject to a large number of large or small external forces. Consequently, it is necessary that the coupling between the components of the battery module be stable. However, the conventional medium- or large-sized secondary battery module cannot perfectly satisfy the above-specified necessary conditions.